tree 705a69af5bc3fddb08476928885297f895c4f501
parent 7f22f6c935cda600660e623a411fe380015d28d9
author Peter Hurley <peter@hurleysoftware.com> 1452494455 -0800
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1453879074 -0800

tty: Fix unsafe ldisc reference via ioctl(TIOCGETD)

ioctl(TIOCGETD) retrieves the line discipline id directly from the
ldisc because the line discipline id (c_line) in termios is untrustworthy;
userspace may have set termios via ioctl(TCSETS*) without actually
changing the line discipline via ioctl(TIOCSETD).

However, directly accessing the current ldisc via tty->ldisc is
unsafe; the ldisc ptr dereferenced may be stale if the line discipline
is changing via ioctl(TIOCSETD) or hangup.

Wait for the line discipline reference (just like read() or write())
to retrieve the "current" line discipline id.

Cc: <stable@vger.kernel.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>